Apparatus and method of sensorless control for synchronous generator

ABSTRACT

An apparatus for controlling a synchronous generator having a converter. A voltage detector detects a terminal voltage of a stator of the synchronous generator. A current detector detects a current flowing through the stator. A rotor position estimating part estimates a rotor position of the synchronous generator from the detected voltage and current. An active power detector detects a active power of the synchronous generator. A reactive power detector detects a reactive power of the synchronous generator or a terminal voltage detector detects an effective value of a terminal voltage of the stator. An active power controller adjusts a q-axis current command to control the active power, and a reactive power controller or terminal voltage controller adjusts a d-axis current command to control the reactive power or terminal voltage.

BACKGROUND OF THE INVENTION

[0001] The present invention relates to apparatuses and methods forcontrolling a synchronous generator and more particular, to an apparatusand method for controlling a synchronous generator without using asensor for detecting the position of a rotor in the generator.

[0002] In order to drive a synchronous machine, a sensor for detectingthe position of a rotor is required in the prior art machine. Meanwhile,there are already proposed several methods of controlling the drivingoperation of a synchronous machine without using a sensor for detectingthe position of a rotor in the machine. Described, for example, inJP-A-9-191698 is a method for estimating a voltage induced in asynchronous machine, estimating a shift angle between the position of arotor of the machine and an estimated value of the rotor position on thebasis of the estimated induced voltage, and correcting the estimatedvalue of the rotor position.

[0003] A control system of a converter for driving the synchronousmachine generally includes a speed control system and a current controlsystem. The speed control system receives a difference between adetected speed value and a speed command, and generates a currentcommand according to the speed command. The current control systemreceives a difference between a detected current value and a currentcommand, and generates a voltage command to the converter according tothe current command.

[0004] However, when a sensor for detecting the position of a rotor isused, a total cost is increased by a cost corresponding to the sensor.Further, since not only the sensor for detection of the rotor positionbut also wiring signal lines for the sensor are required, this leads toan increase in the entire scale of its machine. Furthermore, when thetotal length of the signal lines becomes large, the signal lines willtend to easily carry noise and thus a measure to avoid the noise will berequired. Even when the sensor for detecting the rotor position is notused, on the other hand, the aforementioned rotor position estimatingmethod in the prior art requires estimation of a shift angle between therotor position and an estimated value of the rotor position. For thisreason, the structure of a rotor position estimating block becomescomplicated and thus a calculation time taken for the estimation of therotor position is also prolonged. In the converter control system in theprior art, a change in a resistive value caused by a change intemperature or the like generates an error. When such an error causes anerror in the estimated value of the rotor position, the control accuracyof the converter will drop. This is because the current command isdetermined by the estimated rotor position, in which case thesynchronous machine cannot produce a stable output.

SUMMARY OF THE INVENTION

[0005] It is therefore an object of the present invention to drive asynchronous generator through a simple sensorless control with a shortcalculation time and without using a sensor for detecting the positionof a rotor, accurately control a converter independently of an error inthe estimated value of the rotor position, and produce a stable outputof the generator.

[0006] In accordance with the present invention, the above object isattained by providing an apparatus for controlling a synchronousgenerator which comprises a converter connected to a stator of thesynchronous generator and an inverter connected to the converter andalso connected to a power system. The converter converts a power of avariable frequency generated by the synchronous generator to a D.C.power, and the inverter converts the D.C. power to an A.C. power of afixed frequency. The converter includes a voltage detector for detectinga terminal voltage of the stator of the synchronous generator, a currentdetector for detecting a current flowing through the stator of thesynchronous generator, and a rotor position estimating means forestimating a rotor position of the synchronous generator from a voltagedetected by the voltage detector and a current detected by the currentdetector. The rotor position estimating means calculates a d-axiscomponent of a voltage induced in the synchronous generator in a d-qaxis coordinate system determined by a rotor position during estimationand controls the d-axis component of the induced voltage to zero toestimate the rotor position. The rotor position estimating meansincludes an active power detector for detecting a active power of anoutput of the synchronous generator and a reactive power detector fordetecting a reactive power of the output of the synchronous generator ora terminal voltage detector for detecting an effective value of theterminal voltage of the stator of the synchronous generator The rotorposition estimating means also includes an active power controller forcontrolling the active power of the output of the synchronous generatorwith use of the active power value detected by the active power detectorand an active power controller for controlling the reactive power of theoutput of the synchronous generator or a terminal voltage controller forcontrolling the terminal voltage of the synchronous generator with useof the terminal voltage value detected by the terminal voltage detector.The active power controller adjusts a q-axis current command on the d-qaxis coordinate system determined by the rotor position estimating meansto control the active power of the synchronous generator. The reactivepower controller or the terminal voltage controller adjusts a d-axiscurrent command on the d-q axis coordinate system determined by therotor position estimating means to control the reactive power orterminal voltage of the synchronous generator.

[0007] Other objects, features and advantages of the invention willbecome apparent from the following description of the embodiments of theinvention taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0008]FIG. 1 shows an arrangement of a power generating system to whichthe present invention is applied;

[0009]FIG. 2 is an equivalent circuit of a synchronous generator;

[0010]FIG. 3 shows details of an induced voltage estimator;

[0011]FIG. 4 is a vector diagram (Ed>0) of the synchronous generator;

[0012]FIG. 5 is a vector diagram (Ed<0) of the synchronous generator;

[0013]FIG. 6 is an arrangement of the power generating system to whichthe present invention is applied for control of power factor; and

[0014]FIG. 7 is an arrangement of the power generating system to whichthe present invention is applied, for control of terminal voltage.

DESCRIPTION OF THE EMBODIMENTS

[0015] An embodiment of the present invention will be explained withreference to the accompanying drawings. FIG. 1 shows a generalarrangement of an embodiment of the present invention. In FIG. 1, aconverter 2 is connected to a stator of a synchronous generator 1 andalso D.C. connected to an inverter 4 via a D.C. capacitor 3. Theinverter 4 is connected to a power system via a transformer 5 for systeminterconnection.

[0016] A voltage detector 6 and a current detector 7 are providedbetween the synchronous generator 1 and converter 2, the voltagedetector 6 detecting a terminal voltage across the synchronous generator1, the current detector 7 detecting a current flowing through a statorof the synchronous generator 1. The values of the detected voltage andcurrent are converted to two components of d- and q-axis components by athree-phase/two-phase converter 8.

[0017] The active power detector 9 detects a active power as an outputof the synchronous generator 1 on the basis of two axis componentsignals as outputs of the three-phase/two-phase converter 8. A reactivepower detector 10 detects a reactive power of the output of thesynchronous generator 1 on the basis of the two axis component signalsas the outputs of the three-phase/two-phase converter 8.

[0018] An induced voltage estimator 11 estimates a voltage induced inthe synchronous generator 1 on the basis of the two axis componentsignals as the outputs of the three-phase/two-phase converter 8 as wellas an estimated angular velocity value as the output of an angularvelocity estimator 12. The induced voltage of the synchronous generator1 can be found by correcting a voltage drop caused by the resistivecomponent and synchronous reactance of the synchronous generator 1 fromthe terminal voltage of the synchronous generator 1. The induced voltageestimator 11 outputs an d-axis component in the estimated inducedvoltage.

[0019] An input of the angular velocity estimator 12 is a differencebetween the d-axis component of the estimated induced voltage as theoutput of the induced voltage estimator 11 and zero; while an output ofthe angular velocity estimator 12 is an estimated angular velocityvalue. The angular velocity estimator 12 forms a proportionalintegration control system. An output of the angular velocity estimator12 is limited by a limiter, the upper and lower limit values of thelimiter being determined by an operating speed range of the synchronousgenerator 1. By providing the limiter, the estimated angular velocityvalue of the output of the angular velocity estimator 12 can beprevented from being out of the operating speed range.

[0020] An input of a rotor position estimator 13 is the estimatedangular velocity value as the output of the angular velocity estimator12, while an output thereof is an estimated rotor position value. Therotor position estimator constitutes an integrator. Atwo-phase/three-phase converter 14 performs its converting operation onthe basis of an estimated rotor position value as the output of therotor position estimator 13.

[0021] Explanation will now be made in detail as to the operations ofthe induced voltage estimator 11, angular velocity estimator 12 androtor position estimator 13. For simplicity, explanation will be made inconnection with a cylindrical rotor synchronous generator, but thisholds true even for a silient pole synchronous generator. Shown in FIG.2 is an equivalent circuit of the cylindrical rotor synchronousgenerator. From FIG. 2, Equation (1) which is given below is satisfied,where reference symbol E denotes an induced voltage, V denotes theterminal voltage of the generator, ω denotes an angular velocity, Ldenotes a synchronous reactance, and I denotes a generator current.

E=V+(R+jωL)·I   (1)

[0022] Now Equation (1) is developed in a d-q axis coordinate system.Assuming that Ed denotes a d-axis component of the induced voltage E,E-q denotes a q-axis component of the voltage E, Vd denotes a d-axiscomponent of the generator terminal voltage V, Vq denotes a q-axiscomponent of the voltage V, Id denotes a d-axis component of thegenerator current I, and Iq denotes a q-axis component of the current I;then Equations (2) and (3) are satisfied as follows.

Ed=Vd+R·Id−ωL·Iq   (2)

Eq=Vq+R·Iq+ωL·Id   (3)

[0023] Since the induced voltage estimator 11 outputs the d-axiscomponent of the induced voltage, it is only required to calculate Ed inEquation (2). FIG. 3 shows details of the induced voltage estimator 11.

[0024] Now consider a case of Ed>0. In the case of Ed>0, a vectordiagram of the synchronous generator is given in FIG. 4. In thisconnection, for simplicity of explanation, the resistance of a windingin the synchronous generator is ignored.

[0025] In this case, as shown in FIG. 4, the estimated value of therotor position leads an actual rotor position with respect to phase. Dueto Ed>0, An input to the angular velocity estimator 12 has a negativevalue and the angular velocity estimator 12 forms a proportionalintegration control system, with the result that an estimated angularvelocity value as the output of the angular velocity estimator 12 isdecreased. Since the rotor position estimator 13 constitutes anintegrator, the decrease of the estimated angular velocity value as theinput of the estimator 13 causes a drop of an increase rate in theestimated rotor position value as the output of the estimator 13. As aresult, a phase difference between the actual d-q axes and estimated d-qaxes is decreased to find a phase coincidence therebetween.

[0026] In a case of Ed<0, conversely, a vector diagram of thesynchronous generator is given in FIG. 5, in which case an estimatedrotor position value lags an actual rotor position with respect tophase. Due to Ed<0, an input to the angular velocity estimator 12 has apositive value and the angular velocity estimator 12 forms theproportional integration control system, so that an estimated angularvelocity value as the output of the estimator 12 increases. Since therotor position estimator 13 constitutes an integrator, when theestimated angular velocity value increases as the input of the estimator13, an increase rate in the estimated rotor position value as the outputof the estimator 13 is increased. As a result, a phase differencebetween actual and estimated d-q axes is decreased to find a phasecoincidence therebetween.

[0027] In this way, by calculating a d-axis component in the inducedvoltage of the synchronous generator 1 and controlling the d-axiscomponent of the induced voltage to be zero, the rotor position of thesynchronous generator 1 can be estimated. In accordance with the presentinvention, the need for calculating a shift angle in the estimated rotorposition value can be eliminated and the rotor position can be estimatedwith a simple arrangement.

[0028] An input to a rotational speed controller 15 is a differencebetween an estimated angular velocity value as the output of the angularvelocity estimator 12 and a angular velocity command, and an output ofthe controller 15 becomes a active power command. When the rotationalspeed controller 15 forms, for example, a proportional integrationcontrol system and the angular velocity of the synchronous generator 1is larger than the angular velocity command, the output of therotational speed controller 15 becomes large and the active power of theoutput of the synchronous generator 1 becomes also large.

[0029] As a result, when the active power of the output of thesynchronous generator 1 becomes larger than a mechanical input providedexternally to the synchronous generator 1, its input becomesinsufficient. However, since the insufficient part of the input iscomplementarily supplied from rotational energy, the rotational speed ofthe synchronous generator 1 is decreased and follows the angularvelocity command. On the contrary, when the angular velocity of thesynchronous generator 1 is smaller than the angular velocity command,the output of the rotational speed controller 15 becomes small and theactive power of the output of the synchronous generator 1 becomes small.For this reason, when the active power of the output of the synchronousgenerator 1 becomes smaller than a mechanical input provided externallyto the synchronous generator 1, the input becomes excessive. However,since the excessive input part is stored as the rotary energy of thesynchronous generator 1, the rotational speed of the synchronousgenerator 1 is increased to follow the angular velocity command.

[0030] An input to a active power controller 16 is a difference betweenthe active power command of the output of the rotational speedcontroller 15 and the active power value detected by the active powerdetector 9, while an output of the controller 16 is a active part of thecurrent command to the converter 2. An input to a reactive powercontroller 17 is a difference between a reactive power command providedexternally and the detected reactive power value as the output of thereactive power detector 10, while an output of the controller 17 is areactive part of the current command to the converter 2. The activepower controller 16 and reactive power controller 17 both form, e.g., aproportional integration control system, and the current command to theconverter 2 is determined so that the difference between the activepower command and detected active power value as well as the differencebetween the reactive power command and detected reactive power valuebecome both zero.

[0031] Inputs to a current controller 18 are a detected current value ofthe two axis components as the outputs of the three-phase/two-phaseconverter 8, a active part of the current command of the output of theactive power controller 16 to be sent to the converter 2, and a reactivepart of the current command of the output of the reactive powercontroller 17 to be sent to the converter 2; while an output of thecontroller 18 is an output voltage command to the converter 2. Thecurrent controller 18 forms, e.g., a proportional integration controlsystem, and the output voltage command to the converter 2 is determinedso that a difference between the detected current value and currentcommand becomes zero. Since the output voltage command of the output ofthe current controller 18 to the converter 2 is of two axis components,the output voltage command is converted by the two-phase/three-phaseconverter 14 to a three-phase voltage command.

[0032] A pulse generator 19 outputs a gate pulse signal to the converter2 in a pulse width modulation (PWM) scheme on the basis of a three-phaseoutput voltage command of an output of the two-phase/three-phaseconverter 14 to be sent to the converter 2. The converter 2 receives thegate pulse signal, a semiconductor switching element such as aninsulated gate bipolar transistor (IGBT) performs its switchingoperation at a high speed, and the converter 2 outputs a voltagecorresponding to a command.

[0033] With such an arrangement of the control system as mentionedabove, the rotational speed of the synchronous generator 1 and theactive and reactive powers of the output of the synchronous generator 1can be controlled. When the active power of the output of thesynchronous generator 1 is controlled, the generator can produce astable output.

[0034] On the other hand, when a estimated rotor position value has anerror, it becomes generally difficult to accurately control a converter.This is because a current command to the converter is determined in ad-q axis coordinate system determined by the estimated rotor positionvalue. However, when the active power controller 16 and reactive powercontroller 17 are built in as in the present invention, the convertercan be accurately controlled even when the estimated rotor positionvalue has an error. Explanation will be made as to the operation of thecontrol system of the present invention when the estimated rotorposition value has an error.

[0035] The active power detector 9 and reactive power detector 10 solveEquations (4) and (5), where P and Q denote detected active and reactivepower values in the output of the synchronous generator 1, Vd and Vqdenote d- and q-axis components of the terminal voltage of thesynchronous generator 1, and Id and Iq denote d- and q-axis componentsof a current flowing through the stator of the synchronous generator 1respectively.

P=3/2·(Vd·Id+Vq·Iq)   (4)

Q=3/2·(Vq·Id−Vq·Iq)   (5)

[0036] The three-phase/two-phase converter 8 solves Equations (6) and(13) which are given in the following. In the Equations, θ denotes anestimated rotor position value of the output of the rotor positionestimator 13, VU, VV and VW denote three phase components of theterminal voltage of the synchronous generator 1, IU, IV and IW denotethree phase components of a current flowing through the stator of thesynchronous generator 1, Vα and Vβ denote α- and β-axis components ofthe terminal voltage of the synchronous generator 1, and Iα and Iβdenote α- and β-axis components of a current flowing through the statorof the synchronous generator 1, respectively. An α-β axis coordinatesystem is a coordinate system of two axes fixed to the stator of thesynchronous generator 1. The three-phase/two-phase converter 8calculates to convert three phase detected values to values in the α-βaxis coordinate system with use of Equations (6) to (9) and further toconvert them to values in the d-q axis coordinate system with use ofEquations (10) to (13).

Vα=2/3·(VU−VV/2−VW/2)   (6)

Vβ=2/3·({square root}{square root over (3/2)}·VV−{square root}{squareroot over (3/2)}·VW)   (7)

Iα=2/3·(IU−IV/2−IW/2)   (8)

Iβ=2/3·({square root}{square root over (3/2)}·IV−{square root}{squareroot over (3/2)}·IW)   (9)

Vd=cos θ·Vα+sin θ·Vβ  (10)

Vq=−sin θ·Vα+cos θ·Vβ  (11)

Id =cos θ·Iα+sin θ·Iβ  (12)

Iq=−sin θ·Iα+cos θ·Iβ  (13)

[0037] When Equation (13) is substituted into Equations (4) and (5) withuse of Equation (10), Equations (14) and (15) which follow aresatisfied.

P=3/2·(Vα·Iα+Vβ·Iβ)   (14)

Q=3/2·(Vβ·Iα−Vβ·Iβ)   (15)

[0038] It will be seen from Equations (14) and (15) that P and Q can befound from Vα and Vβ and from Iα and Iβ. Since Vα and Vβ and Iα and Iβare independent of θ from Equation (6) and from Equation (9), further,it will be seen that P and Q are independent of θ. It will beappreciated from the above that, even when the estimated rotor positionvalue contains an error, the active and reactive power detectors 9 and10 can correctly detect active and reactive powers of the output of thesynchronous generator 1. When the active and reactive powers of theoutput of the synchronous generator 1 are correctly detected, the activeand reactive power controllers 16 and 17 can control the active andreactive powers to approach their commands. Thus even when the estimatedrotor position value contains an error, the active and reactive powercontrollers 16 and 17 determine the current command in such a manner asto correct the error. Thus even when the estimated rotor position valuecontains an error, the converter 2 can be accurately controlled.

[0039] Next an embodiment when the power factor of the synchronousgenerator 1 is controlled is shown in FIG. 6. When the reactive power ofthe output of the synchronous generator 1 is controlled, the powerfactor of the synchronous generator 1 can be controlled. Since the powerfactor of the synchronous generator 1 can be controlled by adjusting aratio between the active and reactive powers of the output of thesynchronous generator 1, its reactive power command can be given bymultiplying its active power command by a gain.

[0040] Inputs to a gain setter 20 are the active power command as theoutput of the rotational speed controller 15 and the estimated angularvelocity value as the output of the angular velocity estimator 12; whilean output of the gain setter 20 is the reactive power command to theconverter 2. The gain setter 20 adjusts the gain to be multiplied by theactive power command according to the estimated angular velocity valueand outputs the value of multiplication between the adjusted gain andactive power command as the reactive power command.

[0041] When the estimated angular velocity value is low, the gain setter20 adjusts the gain in such a manner that the induced voltage andcurrent of the synchronous generator 1 coincides with each other intheir phase. In this way, such gain adjustment enables operation of thesynchronous generator 1 with a high efficiency and with a smallgenerator current in a low rotational speed range of the generator 1.

[0042] When the estimated angular velocity value is high, on the otherhand, since the induced voltage of the synchronous generator 1 becomeshigh, the terminal voltage of the synchronous generator 1 also becomesgenerally high. When the terminal voltage of the synchronous generator 1becomes high, there may sometimes occur such a situation that thegenerator cannot be operated due to an overvoltage. To avoid this, whenthe estimated angular velocity value is high, the gain setter 20 adjuststhe gain in such a manner that the current of the synchronous generator1 lags the induced voltage of the synchronous generator with respect tophase. When the gain is adjusted in this way, the terminal voltage ofthe synchronous generator 1 can be made low and the synchronousgenerator 1 can be operated in a high rotational speed range of thegenerator 1 with an increase in the terminal voltage of the generator 1being suppressed.

[0043] As mentioned above, by controlling the power factor of thesynchronous generator 1, the synchronous generator 1 can be operatedwith a high efficiency and the increase of the terminal voltage of thegenerator 1 can be suppressed.

[0044] Further, the terminal voltage of the synchronous generator 1 canbe directly controlled. An embodiment when the terminal voltage of thesynchronous generator 1 is controlled is shown in FIG. 7. The embodimentof FIG. 7 is basically the same arrangement as that of the embodiment ofFIG. 1, except that the reactive power detector 10 in FIG. 1 isconnected to a terminal voltage detector 21 and the reactive powercontroller 17 is changed to a terminal voltage controller 22.

[0045] The terminal voltage detector 21 detects the effective value ofthe terminal voltage of the synchronous generator 1 on the basis of twoaxis component signals as the outputs of the three-phase/two-phaseconverter 8. An input to the terminal voltage controller 22 is adifference between a terminal voltage command provided externally and adetected terminal voltage value as the output of the terminal voltagedetector 21, while the output of the terminal voltage controller 22 is areactive part of the current command to the converter 2. The terminalvoltage controller 22, which forms, e.g., a proportional integrationcontrol system, determines a reactive part of the current command to theconverter 2 in such a manner that the difference between the terminalvoltage command and detected terminal voltage value becomes zero.Adjustment of the reactive part of the current command to the converter2 enables adjustment of the power factor of the synchronous generator 1and enables control of the terminal voltage of the synchronous generator1.

[0046] The terminal voltage detector 21 performs its calculation inaccordance with Equation 16, where Vt denotes a detected value of theterminal voltage of the synchronous generator 1, and Vd and Vq denote d-and q-axis components of the terminal voltage of the generator 1respectively.

Vt={square root}{square root over ((3/2))}·{square root}{square rootover ((Vd·Vd+Vq·Vq))}  (16)

[0047] Substituting Equations (10) and (11) into Equation (16) satisfiesEquation (17).

Vt={square root}{square root over ((3/2))}·{square root}{square rootover ((Vα·Vα+Vβ·Vβ))}  (17)

[0048] It will be seen from Equation (17) that Vt is found from Vα andVβ. It will also be seen from Equations (6) and (7) that, since there isVα and Vβ are not dependent on θ, Vt is not dependent on θ. From theabove, it will be appreciated that, even when the estimated rotorposition value contains an error, the terminal voltage detector 21 cancorrectly detect the effective value of the terminal voltage of thesynchronous generator 1. When the detector 21 can correctly theeffective value of the terminal voltage of the synchronous generator 1,the terminal voltage controller 22 can control the terminal voltage toapproach its command. Thus even when the estimated rotor position valuecontains an error, the terminal voltage controller determines thereactive part of the current command in such a manner as to correct theerror amount. For this reason, even when the estimated rotor positionvalue contains an error, the converter 2 can be accurately controlled.

[0049] The apparatus can be made small in size without using a rotorposition detecting sensor by driving the synchronous generator under thesimple sensorless control. Further, the converter can be accuratelycontrolled independently of an error included in the estimated rotorposition value. Furthermore, the generator can produce a stable outputby controlling the active power. In addition, the synchronous generatorcan be operated with a high efficiency or the terminal voltage of thesynchronous generator can be controlled by controlling the reactivepower.

[0050] It should be further understood by those skilled in the art thatthe foregoing description has been made on embodiments of the inventionand that various changes and modifications may be made in the inventionwithout departing from the spirit of the invention and the scope of theappended claims.

What is claimed is:
 1. An apparatus for controlling a synchronousgenerator which comprises a converter connected to a stator of saidsynchronous generator and an inverter connected to said converter andalso connected to a power system and wherein said converter converts apower of a variable frequency generated by said synchronous generator toa D.C. power, and said inverter converts said D.C. power to an A.C.power of a fixed frequency, said converter includes a voltage detectorfor detecting a terminal voltage of the stator of said synchronousgenerator, a current detector for detecting a current flowing throughthe stator of said synchronous generator, and rotor position estimatingmeans for estimating a rotor position of said synchronous generator froma voltage detected by said voltage detector and a current detected bysaid current detector, said rotor position estimating means calculates ad-axis component of a voltage induced in said synchronous generator in ad-q axis coordinate system determined by a rotor position duringestimation and controls the d-axis component of said induced voltage tozero to estimate the rotor position, said rotor position estimatingmeans includes an active power detector for detecting a active power ofan output of said synchronous generator and a reactive power detectorfor detecting a reactive power of the output of said synchronousgenerator or a terminal voltage detector for detecting an effectivevalue of the terminal voltage of the stator of said synchronousgenerator, said rotor position estimating means also includes a activepower controller for controlling the active power of the output of saidsynchronous generator with use of the active power value detected bysaid active power detector and an active power controller forcontrolling the reactive power of the output of said synchronousgenerator or a terminal voltage controller for controlling the terminalvoltage of said synchronous generator with use of the terminal voltagevalue detected by said terminal voltage detector, said active powercontroller adjusts a q-axis current command on the d-q axis coordinatesystem determined by said rotor position estimating means to control theactive power of said synchronous generator, said reactive powercontroller or said terminal voltage controller adjusts a d-axis currentcommand on the d-q axis coordinate system determined by said rotorposition estimating means to control the reactive power or terminalvoltage of said synchronous generator.
 2. An apparatus for controlling asynchronous generator as set forth in claim 1, further comprising anangular velocity estimator for receiving a difference between a d-axiscomponent of the induced voltage of said synchronous generator on thed-q axis coordinate system determined by said rotor position estimatingmeans and zero, and wherein said angular velocity estimator forms aproportional integration control system.
 3. An apparatus for controllinga synchronous generator as set forth in claim 2, wherein an output ofsaid angular velocity estimator is limited by a limiter and upper andlower limit values of said limiter are determined by an operating speedrange of said synchronous generator.
 4. An apparatus for controlling asynchronous generator as set forth in claim 3, further comprising arotor position estimator for receiving an estimated angular velocityvalue as an output of said angular velocity estimator, and wherein saidrotor position estimator forms an integrator.
 5. A method forcontrolling a synchronous generator in an apparatus which comprises aconverter connected to a stator of said synchronous generator and aninverter connected to said converter and also connected to a powersystem and wherein said converter converts a power of a variablefrequency generated by said synchronous generator to a D.C. power, andsaid inverter converts said D.C. power to an A.C. power of a fixedfrequency, said converter includes rotor position estimating means,reactive and active power controllers and a terminal voltage controller;said method comprising the steps of: estimating by said rotor positionestimating means a rotor position of said synchronous generator from aninduced voltage of said synchronous generator and a current of thegenerator flowing through the stator of the generator; calculating ad-axis component of a voltage induced in said synchronous generator in ad-q axis coordinate system determined by a rotor position duringestimation and controlling a d-axis component of said induced voltage tozero to estimate the rotor position; controlling by said active powercontroller a detected active power value of the output of saidsynchronous generator; controlling by said reactive power controller orterminal voltage controller an detected reactive power value of theoutput of said synchronous generator or a detected terminal voltagevalue of said synchronous generator; adjusting by said active powercontroller a q-axis current command on the d-q-axis coordinate systemdetermined by said rotor position estimating means to control a activepower of said synchronous generator; and adjusting by said reactivepower controller or said terminal voltage controller a d-axis currentcommand on the d-q-axis coordinate system determined by said rotorposition estimating means to control a reactive power or a terminalvoltage of said synchronous generator.